Airplane wing and slotted flap



June 13, 1950 w, w ms 2,511,504

AIRPLANE WING AND SLOTTED FLAP Original Filed July 2, 1942 v s Sheets-Sheet 1 uvmvrox. WILLIS M. HAWKINS Agent June 13, 1950 w. M. HAWKINS I 2,511,504

AIRPLANE WING AND SLOTTED,FLAP

Original Filed July 2, 1942 3 Sheets-Sheet 2 lss/um/lsl s I50 I35 \41 nvwszvrox. I WILLIS M. HAWKINS M Agen W. M. HAWKINS AIRPLANE WING AND SLOTTED FLAP June 13, 1950 3 Sheets-Sheet Original Filed July 2, 1942 INVENTOR. WILLIS M. HAWKINS Agent S is faired into the top of the fuselage by means of a tapered fin in which extends back from the transparent canopy ll of the pilots come partment l2.

The landing gear which is preferably of the so-called tricycle type, comprises two laterally spaced non-steerable main landing wheels retractably carried from the lower surface of the fuselage F and positioned to the rear of the center of gravity of the airplane by suitable outwardly extending shock absorbing strut l6, and a forward landing wheel ll preferably retractably carried from the nose of the fuselage by means of a suitable shock absorbing strut l8, said forward Wheel being free to swivel about the axis of the supporting strut whereby the airplane can be steered on the ground by means of difierential application of the brakes in the main wheels or by means of suitable linkage between rudder foot pedals and the forward strut column.

The engine for driving the propellers and various accessories is centrally located and housed.

within the fuselage in the position diagrammatically indicated by dotted lines 20, and transmission of power to a pair of outboard tractor propellers, carried on the leading edge of the main wing on either side of the fuselage, one of which is shown at 2|, is accomplished by means of a pair of drive shafts 22 and 23 extending laterally from the engine gear box 24 and into the wings. The power from the shafts 22 and 23 is transmitted to the propellers through suitable gear and shaft combinations, one of which is best shown in Figures 2 and 3, and comprises an overrunning or so-called one-way clutch 25, a pair of suitable bevel gears 26 and 21, and an axially positioned propeller shaft 28 which is journaled in suitable bearings 29, 30, and 3| within the main wing W1.

Also housed within the main wing, in one embodiment of the invention as best shown in sectional view in Figure 3, are boundary layer removal fans, one of which is shown at 35, mounted on a shaft 36 which is rotatably carried in suitable bearings 37 and 38 within the wing and driven by means of a gear train comprising a driven pinion 39 fixed on the fan shaft 36 and a driving gear 45 fixed to the rearward extension 4| of the beforementioned propeller shaft 28. The overrunning clutch 25 is so constructed and arranged as to transmit torque through from the engine to the propeller shaft, but upon reduction of the power output and speed of the engine below that required for propulsive effort by the propellers for a given air speed of the airplane, the said propeller and the said boundary layer fan can continue to rotate at a higher speed than that corresponding with the engine speed or under so-called free-wheeling conditions. The overriding clutch may be of any suitable construction; for example, the conventional automatically operating roller and cam type well known in the automotive industry.

The main wing W1 is provided with airlerons 45, leading edge variable area slots 48, for lateral control, and trailing edge flaps 46 for modification of the lift characteristics of the wing. The said trailing edge flaps 46 are fixed to hollow torque tubes as shown at 41 by means of which they are pivotally hinged in the wing and are adapted to be rotated from their normal raised or fully retracted'positions as shown in Figure 3 to their fully lowered position shown in Figure through suitable worm and gear couplings 5| upon the inner root ends of said torque tubes 41.

Each of the trailing edge flaps as shown at 46 is provided with curved passageways or ducts 53 extending throughout its length, located to the rear of the said torque tube and extending through the fiap from the top to the bottom surfaces. A rearward extension 55 of the lower wing skin surface forms a stationary stnip or valve-likeelement which bridges and normally closes the lower openings to the said fiap passages 53 when the flap is fully up as shown in Figure 3, thereby forming a, closed and continuous lower surface to the trailing edge, but when the flap is lowered to the position shown in Figure 4, the tongue 55 swings into the flap passage, thereby opening a free air passageway therethrough from the lower surface to the top surface of the flap. When the flap 46 is in it fully raised position as shown in Figure 3, the flap passages 53 are in communication with the duct 56 within the wing structure on the suction side of the boundary layer .removal fan 35 by way of a series of perforations 51 longitudinally spaced along the length of the rearward wall of the flap torque tube and a series of oppositely positioned perforations 59 through the opposite 7 forward wall of the torque tube. When the trailof the torque tube 41 is placed in communication with the beforementioned duct 56 leading to the suction side of the fan 35. In this arrangement the torque tube 41 is closed at the ends to confine the inward air flow to that removed through the perforations and flap slot.

The leading edge slots 48 of the main wing are constructed and preferably operated in conjunction with the trailing edge flaps 46 in the same manner as those of the forward wing W2 hereinafter fully described, mainly in connection with Figures 2, 6 and 7.

In an optional arrangement as shown in Figure 10, instead of employing separate boundary layer fans in each wing, a single centrally located fan 65 within the fuselage may be employed, said fan being driven by the engine 20 through an axially positioned auxiliary shaft 66. The suction side of the said fan 65 is closed off from within the fuselage by'means of a suitable bulkhead 6'! and a venturi shaped fan housing 68 to form a chamber 69 into which the inner root ends 10 and II of the beforementioned flap torque tubes 41 extend through suitable packing seals, one of which is best shown at 12 in Figure 9. With this arrangement the innermost perforations 60 (see Figures 3 and 4) may be omitted from the torque tube walls as shown in Figure 5, since communication with the boundary layer removal fan is in the latter arrangement efiected entirely through the bore of the flap torque tube.

4, by means of motors located within the fuselage In the arrangement of Figure 2 in which individual fans are provided in each wing, each fan discharges into a laterally extending duct, one of which is shown at 15, which in turn communicates with a plurality of rearwardly directed boundary layer control slots as shown at 1B suitably placedflin the forwardregion 'of'the upper skin of thewing.

. In the optional arrangement ofFi'gure' 10,the

fan .65 discharges into a chamber 11' within the.

connecting the said chamber 11 and the beforementioned boundary layer-control slots as shown at 16in the wing.

In either of the beforementioned boundary layer removal arrangements, provision is made as best shown in Figures 8"and 9, for withdrawal of boundary layer airfrom the rear portion of the wing fllletadjacent the fuselage and in line with the flap hinge line. A slot 82-is provided'in the wing fillet 83 which is placed in communication with the boundary removal fan by way of'a perforation 84 in the flap torque tube 41. I M

ln the forward part of the fuselage-F isf theb'eforementioned pilots :compartmnt;"as shown at I2 containing the pilot s' seat 9 I and a conventional wheel type control column 92 pivotally supported at its lower end at 93 in 'ja suitable bearing mounting 94 fixedto the ruseiage structure at 95 and 91 is 'adapted tobe controlled by means of a reciprocable pilot'iod linked to the control column 92 at 99, and which extends into the cylinder to. adiiferential' controlvalve located in the piston I00; Thebo'oster-servo device may be any one of several types welbknown in'the industry which operates preferably on the hydraulic principle and. is adapted -to' amplify and transmit the ampIifiedf rces toQthe airplane con trol surfaces which are proportional to -the forces applied by the pilot.

Fluid under pressure and controlled-by the said differential valve, 'actuate's thes'afid-pistonl00 which, in turn, through piston rod IN and lever I02, serves as a'booster 'to mov'e' and-* c'ontrolthe' attitude of the horizontal stabilizer W2 asmore fully described hereinafter.

Referring now primarily toIEigi'i'r'es" 10 and 11, the forward wing or horizontal stabil'izer -W2= is' pivotally supported in its entirety upon-arc tatable spanwise positioned tubular spar of com-- pound construction comprising two concentric tubes 85 and 06. The exterior-tube-85 of-greater diameter which is composed-of two coaxial sections joined end to end by means-of a special flangedconnection as shown at 81, 'is rotatab1y supported within the fuselage upon a pair ofoppositely positioned bearings, one of which is shown at I05attached to the inside surfaceofthe fuse-i the ends of tube, 85 into the horizontal stabilizer ne t s w e it i on-.r t tab rfixed i h,

spect to a wins y u table flansedtqme o such as shown at, I09 and III! attachedto the wing ribs lllfand H2.

The beforement' ned specialifianged qnpe'eeon 81 is formed with an gfil annu ar :shapd recess 1 I4 adapted tohou'se anannular'shaped'recess I I5 whichis f xed to and 'rdrm ajc ejf ralportion of the innermost t be as. The flanged con nection 8T also "carries aleve 6: thebeforeme'ntioned booster control piston rod I0I is pivotally attached at I03.

Fixed to the lever I02 and radially positioned" with respect to the center of the flange coupling 81' isa hydraulic cylinder I I6 containing a piston I'I'l and'a piston rod I I8 extending from the lower end thereof. 'The'piston is adapted to be actuated'by hydraulic pressure which may be applied to either end of the piston IIT through flexible tubular "connections H9 and I20. The flange .81"

is provided with a cam-like recess I2I ofsemicircular contour and having a centrally located depression I22 of approximately semi-cylindrical shape. The lower end of the beforementioned piston rod H8, which is provided with a semi-- cylindrical shaped follower tip I23 adapted to bear on the cam surface I2I and to fit into-the cam depression I22 extends into the recess I22 through'a coaxial hole I24 in the peripheryof the flanged connection 81. v A

A bevel gea'r I26 is fixed to the outer spar tube intermediate the rib I08 and fuselagefillet'l21 and meshes with a bevel pinion I28 which is carried on the forward end of a shaft I29 rotatably pinion I38 which meshes with a bevel gear I39 fixed on the end of the hinge pin I40 of a trailing edge tab surface MI. The said trailing edge tab I 4 I is hinged at I42 and I43 and adapted to be swung at an angle above and below the level of the surfaces of the flap I35.

Referring now primarliy to Figures 6 and 7, the

forward wing 'VV2 carries semi-automatically operating variable area leading edge slot I 45 comprising a movable leading edge slot 146 supported upon a plurality of rods, one of which is shown at l'fel'and each of which make a slidingfit in the forward'portion of the airfoil in a pair of'suitable: supports as shown at I48 and I49 for limited 1on gitudinal reciprocative movement. Figures 6 and '7 show the leading edge slot in its fully closed and fully opened positions respectively.

The" trailing edge of the horizontal stabilizer is provided with slotted trailing edge flaps as shown at I35 constructed similar to those hereinbefore' described in connection with the main wing W1. These slotted flaps I35 are pivotally mounted upon coaxial torque tubes as shown at I50 and I 5|, which are adapted to be rotated through the limited flap lowering angle as indicated, by suitable means such as by an electric motor I52 acting through a worm and gear drive located within the pivotable' wing section in the position'shown at !53 'in Figure 2, andas best shown in section I53 in Figures 6, 7, and 11.

Eccentrically pivoted to the gear I54 at I55 ;is

- a linkage rod I56 which extends forward through porting rod I41 when the trailing edge flap I35 is up as shownin Figured, and release said tongue, and the leading edge slot mechanism associated therewith when the'trailing edge flap is fullylow ereaessnown inn-me v. v

fin the forward wing VVz the trailing edge flap I35 may have the same construction as that of the main wing as shown in Figure 4, and provision accordingly made for withdrawing the boundary layer through the perforations in the torque tube and into the interior sealed cavity I63 of the airfoil as best shown in Figures 4, 6, and 7, and thence through a plurality of perforations as shown at I6 3 and I85 into the tubular spar 86. From there the air flows inwardly toward the fuselage through the tubular spars 85 and 86, and through a plurality of registering perforations in tubes 85 and 85 as shown in'IBB, to the longitudinal passages shown at I69 and Ill] on each side of the fuselage adjacent the fuselage skin surface and thence rearwardly to the suction duct 69 of the beforementioned boundary layer removal fan 55 thence to be finally exhausted through the plu rality of main Wing slots I5 as before mentioned.

The operation is as follows: 7

The airplane, while at rest onthe ground and at the start of the take-off run, is initially in the attitude substantially as shown in Figure 1. During the take-off run the main wing trailing edge flaps 45 may be maintained in a full-up position, or if desired to reduce the take-off run and speed, they may be partially lowered to increase the maximum coefficient of lift of the main wing W1. Upon approaching minimum flying speed, the forward wing W2 is pivoted by pulling 1) back on the control column, to increase its angle of attack while at the same time, the trailing edge flap may be partially lowered by means of the motor I53 to a position preferably intermediate that shown in Figures 6 and 'T at which position the leading edge flap will be released for automatic action. As the lift on the forward wing W2 is thus increased, the load on the landing gear will be gradually reduced until the forward wheel I! is raised off the ground,'thereby increasing the angle of attack of the main wing sufiicient to effect a take-off from the ground surface. During the initial high angles of attack of the forward wing the leading edge slot will, upon lowering the trailing edge flap and the resultant releasing of the latch I6I, automatically move forward to open the variable slot I45, thereby increasing the angle ofincidence to which the forward wing may be moved without stalling. Thus, by the combined use of the trailing edge and leading edge slots, the maximum effective coeflicient of liftof the forward wing may be greatly increased to the value necessary for adequate control. As

the airplane gains a margin of flying speed immediately following the take-off, the angle of incidence of the forward wing may then be reduced and the resultant increase in air pressure at the leading edge immediately effects automatic closing of the leading edge slot. Subsequent raising of the trailing edge flap actuates the latch mechanism to lock the said leading edge slot closed during normal high speed flight. The trailing edge flap of the main wing may then also be raised to its normal full-up position.

In the landing maneuvers of the airplane the before described operations are, in substance, reversed. However, in landing, the degree to which these controls are employed is, in general, greater than that for take-off. .For example, as the air speed is reduced preparatory to landing, the trailing edge flaps of the main wings may be lowered to the extreme positions shown in Figure 4 to effect a maximum possible coefficient of lift of the said main wing, and at the same time to effect a maximum drag coefiicient. In so doing, the effective center of lift of the main wing will be moved rearward, thereby placing an increased diving moment upon the aircraft. Due to the combined efifect of this increased diving moment and to the inherently more rapid falling off of the lift of the low aspect ratio forward wing with decreasing speed, it is then necessary in order to maintain stability at the increased angles of attack and accompanying reduced speeds to greatly increase the maximum effective coefficient of lift of the forward wing and also the maximum angle of incidence at which its lift can be maintained. This is then accomplished by fully lowering the trailing edge flaps of the forward wing, releasing the leading edge slots and increasing the effective angle of attack of the entire forward wing, carrying said flap and leading edge slot. The accompanying boundary layer control on either or both the main and forward wings further aug ments their high lift characteristic and prolongs the control of the aircraft at reduced speeds.

For full control of the airplane under all conditions, it may be desirable to provide for rotation of the forward wing through an angle of approximately +20 to 20 with respect to the longitudinal axis of the airplane as indicated in Figures 6 and 7.

Preparatory to flight operations, hydraulic pressure is initally applied to the top of cylinder IIB through tube IE9 from a suitable pressure source to force the piston Ill and piston rod IIB downward. The resultant pressure between the follower I23 and the, cam surface I2I will cause relative angular rotation between the flange II5 of the tube 86 and the flanged housing 81 of the 5 tube 85 until the said follower I23 falls into the depression I22, thus locking the two tubular spars 85 and 86 together against further relative angular displacement. Control forces now applied to the lever I02 through the booster control rod It! will be tortionally transmitted directly through both of the concentric tubular spars 85 and 83 to the horizontal stabilizer wings. During low speed maneuvers such as at take-01f, the entire horizontal stabilizer is preferably directly connected through for positive and rapid pivotal movement.

During flight at intermediate airspeeds, as after attaining a margin of speed following take-01f, or during prolonged cruising at speeds of maximum economy, during which time a maximum degree of stability and ease of control is desirable, the control of the horizontal stabilizer may be shifted to an indirect application of controlling forces as follows: The formerly applied hydraulic pressure is released from the top of. cylinder IIB through line I I9 and applied to the lower end of said cylinder through line I20 to raise the piston rod II8 upward to release the cam I2I from the follower I23.

The flange H5 is thus unlocked from the housing 81 to allow relative angular rotation between the spar tubes 85 and 88 through an angle a. as determined by the width of the cam surface depression I2I. At the highest position of the piston II! in the cylinder I It, the cam follower I23 extends into the cam cavity within the housing 87 to prevent relative rotation between flange H5 and said housing 81 exceeding that determined by the width of said cam depression.

' Under these conditions the horizontal stabilizer when are preferably approximately from 20 '1-t0--e20 withirespeotato the-longitudinal axis of theifusela'ge.

Now, movement :of the controls-subsequent to 1 such. release, results in. rotationxof' the outer spar tubei85 relativeto theinner tube"86'-,' which will further result. in tro'tationof .bevel' gear I26 with :respectto the-bevel pinion I28, thus imparting through shafts 'l 29 an'd l36,'-and through gears 'I38'and' I39 angular displacement to the trailing "'ed'ge'tab Ml. .By this means the said tab MI is operated to control the'angleof attack of the freely floating horizontal stabilizer. Under such conditions, the airplaneis exceedingly stable in pitch by reason 'of the. constant coefficient of llftmaintained' bythe .fioatin'g stabilizer for any given tab setting. I

At higher air speeds approaching. sonici-veloc- Iities, it maybe desirable to again return. the controls to the direct locked connection with the T booster system for the reasonthat, as before stat- ..ed,.trailing.edge flaps tend to become ineffective :meansnfor varying the ooeflicient of liftof an :airfoilunder the criticalair flowconditions enthe removal fan 35. Whenth'etra-iling edge flaps "lfiareup' as'show'n inFigureB, the boundary layer air' is drawn into the'upper' opening of slot '53 and thence through 'YpeI'fQrations" 51 and 59 into' the fan: inlet'or'suction' chamber 56 in the --wing. From fan '55 the air' is exhausted into the lateral duct-l5, and thencedischarged"rearwardly over the outer upper'surface of'the wing through the rearwardly directed discharge slots 16.

"'When the trailing erl'ge'flap is" in a fully lowered position as shown in-Figures t and '7, the'boundary layer air is" w-ithdrawn fromthetop of'the wing through the plurality of" torque tube perforations exposed at 59 and thence throughper forations 6B to'the suction of the boundary layer removal fan 35 and out as before described. In "this fully lowered position, the slot 53 is cut off from the torque tube perforations 51 as best shown in Figure 4, and the slot 53 opened by the inward swing of the torque "55 to allow airflow through from the lowersurface of the wing to the upper surface of thewing tothe upper surface of the trailing edgeflap.

The boundary layer removal fan 35 is normally driven at high speed by the engine 26 through'the laterally extending propeller drive shafts 23, clutch 25 and the gears 26, 21, 39 and Ml, within the wing.

In case of engine failure, or in any event during the gliding approach and. landing maneuvers when the engine is either stopped or -is idling, provision is made'inthepresent invention for maintaining a continuation of the effective operation of the boundaryv layer removal apparatus. Referring again to Figures 2 and 3, in event of such engine failureorengine idling, the overriding clutches as shown at 25 in the lateral drive shafts 22 an'd23 act to cutthe engine out ofdriving connection with the propellers and to allowithepropellers to continue: rotation in the relative air-stream in a so-called free wheeling relationship with respect to the engine. Under such conditions the propeller is free to act as a wind-driven motorabsorbing power from the airstream' and delivering it through the propeller shaft 28-, gear 40 and pinion 39, and through shaft 36 to the boundary layer removal fan 35. The ratio of the gears 40 and 39 is preferably such as to step-up the speed of the fanwith I respect to the propeller, and in'this connection, the propeller is preferably of a controllable pitch type in which the pitch of the blades may be adjusted by the pilot during flight to obtain the required torque and power inputfor the proper 10 boundary layer removal fan operation. This'is desirable, since the propeller blade setting for eflicient propulsion in normal flight is usually not the best setting for proper operation of: the propeller as a wind-driven power-producing machine.

In the optional arrangement for boundary layer air removaLas best shown in Figures 10 and 11, the single boundary layer removal fan 65, located centrally in the fuselage, is adapted to be driven by the longitudinally positioned auxiliary shaft 66 extending from the gearbox '24 of the engine 20. The boundary layer air in this optional arrangement is withdrawn into the flap torque tubes through slot 53 and perforations '51 and 59, in the'manner before'described in connection with Figures 4, 6; and 7. However, in this modified arrangement, the perforations 60 are omitted and a flap I'H provided adjacent the flap hinge to close theperforations 59 from communication with the interior of'the wing as best shown in Figure 5. The boundary layer air which thus enters the torque tube, flowsinwardly toward the fuselage through the flap torque tubes, and through the innermost open rootends Ill and H of the said" torquetubes' into the suction inlet chamber 59-of the fan 65.

The boundary layer air from fan-65 is discharged at increased pressure into the chamber -1'|'from which it is conducted out through the 49 lateral ducts 80 and 81,- and discharged through the rearwardly directed boundary layer control discharge slots as shown at 16. r

In the forward wing W2, the boundarylayer .may beremoved from the upper surfaceof the -wing-by withdrawalintothe interior portionof thawing through perforations in the flap torque 'tube in-themanner' described for-the main wing *in connection with Figures 2, "3, and 4. .As best shown in Figures 6,-7, and: 11, the thus withdrawn lio-boundarylayer is'exhausted from the said interior of the forward wing W2 through a series of "suitable perforations'in the tubular spar to the *registering'ports H36 in tubes 85- and '86, and-from these into the beforementioned longitudinal-pas- "sages [-69 and-110 on eithersideof the fuselage which lead-rearwardly-tothe opening H5 into -the-suct-ion chamber-69 #of theboundary layer removal fan 65.

Removal=of theboundarylayer' air, not only from the uppersurfaceof: the wing, but also'from the upper fillet provided at the point of intersectionof the wing-with the fuselage, as shown in Figures--8---and-9,-has been found to be efi'ective-in delaying-incipient stalling conditions of 05 the-airflowover-the-entire upper {surface of the wingat high-angles of attack. This appearsto be-duetothvfactthat the-region of-the wing root --adiacentthe fuselage is the -most critical one and the point from which initial stalling conditionsprogress to the-*other-portion ofthe wmg.

Hence, delay of stalling at't-he wi ngroot delays theestalling :of the entire wing. The boundary layer air removal maybe advantageously utilized 7 in connection with the wings'and wingfillets of l1 either or both themain wing or the forward Horizontal stabilizerf Some'of the advantages of the present invention are: the'landing or stalling effective coefiicientof lift of the airplane as a whole is in- "creased over that of more conventional types by reason of the fact that the controlling force on *theforward horizontal stabilizer is a positive lift- 'ing' force as compared to the downward tail load "onthe conventional rearward tail type of airplane. Similarly in the present invention, the horizontal stabilizer trimming load for steady flight conditions is in the same direction as the main wing load thus rendering the win load factor always less than the airplane load factor. The opposite of this condition obtains in a conventional airplane where the wing load must also W include the lift equivalent of an opposing tail load. Control at take-off is improved due to the fact that when the nose lifted' by the forward horizontal stabilizer, the reaction on the main wing is immediately reduced and is much smaller than on an ordinary tricycle landing gear airplane of conventional wing arrangement where a down load must 'be initially applied behind the main gear. This not only reduces the amount of trim adjustment required to attain a takeoff attitude, but also reduces the load on the Wheels and the accompanying drag.

Other advantages reside in the novel manner of employment of boundary layer control as here- 'inbefore described to increase the speed range and also the efliciency of flight of the airplane, and in the novel variable stabilizer whereby maximum positiveness in longitudinal control with minimum effort may be accomplished.

The, foregoing is merely illustrative of the apparatus and method of operation of the invention and is not to be limiting. The invention includes any apparatus and method which accomplishes the same; results within the scope of the claims.

I claim: g

1. In an airplane wing, the combination comprising: a pivotally supported trailing edge flap adapted to be moved through an angle between a normal raised and lowered position, an air slot extending through said flap at a point adjacent and to the rear of the pivot of said flap, a stationary rearward extension of the lower surface of the wing normally bridging the lower opening.

of said air slot when the said flap is in a raised position, and adapted to project into said slot opening relative to said flap to open said air slot when the flap is lowered, and means to rotate said flap about its pivotal support through a predetermined angle to rais and lower the trailing edge thereof.

2. In an airplane wing the combination comprising: a pivotally supported trailing edge flap, an elongated air slot extending through said flap at a point adjacent and to the rear of the pivot line of said flap, a stationary rearward extension of the lower surface of the wing projecting to the rear of said pivot line and normally bridging the lower opening of said air slot when the said flap is in a raised position and adapted to project into said slot opening relative to said flap to open said air slot when the flap is lowered and means to rotate said fiap about its pivotal support through a predetermined angle to raise and lower the trailing edge thereof.

' 3. In an airplane the combination comprising: a pivotally supported trailing edg flap, an elongated air slot extending through said flap at a point adjacent and to therear of the pivot line of said flap, a stationary rearward extension of the lower surface of the wing projecting to the rear of said pivot line and normally bridging the lower opening of said air slot when the said flap is in a raised position and adapted to project into said slot opening relative to said flap to open said air slot when the flap is lowered, and means communicating with said slot to withdraw boundary air from the upper surface of said wing inward through the upper portion of said slot when said flap is in a raised position and means to cut 011 communication of said means with said slot when said flap is in a lowered position.

4. In an airplane wing, the combination according to claim 3, in which the means communicating with said slot comprises a tubular hinge member upon which the flap is pivotally mounted, openings communicating between said slot and the interior of said tubular hinge member, means adapted to withdraw air from said slot through said tubular hinge member when said flap is in a raised position, and means adapted to close said openings communicating between said slot and the interior of said tubular hinge member when said flap is in a lowered position.

5. In an airplane wing, the combination according to claim 3, in which the means communieating with said slot comprises a tubular hinge member uponwhich the flap is pivotally mounted, openings communicating between said slot and the interior of 'said'tubular hinge member, means adapted to withdraw air from said slot through said tubular hinge member when said flap is in a raised position, means adapted to close'said openings communicating between said slot and the interior of said tubular hinge member when said flap is in a lowered position, and a second slot communicating between the upper surfac of said wing and the interior of said tubular hinge member when said flap is in a lowered position, said second slot being located forward of said first mentioned slot and adjacent the said hinge line of said flap. i

6. In an airplane wing, th combination according to claim 3, in which the said tubular hinge member comprises a torque tube extending from the said wing into the fuselage of the airplane and by means of which the flap i actuated and pump means in said fuselage connected with the ends of said torque tubes for withdrawing air through said torque tube from said slots.

WILLIS M. HAWKINS.

REFERENCES jorrEn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,726,118 Page Aug. 27, 1929 1,829,616 Stalker .Oct. 27, 1931 1,830,122 Milburn Nov. 3, 1931 2,041,792 Stalker May 26, 1936 2,169,416 Griswald, 2d Aug. 15, 1939 2,222,915 Rebeski Nov. 26, 1940 2,334,975 Williams Nov. 23, 1943 2,340,396 McDonnell, Jr. Feb. 1, 1944 2,406,916 Stalker Sept. 3, 1946 2,406,917 Stalker Sept. 3, 1946 2,406,918 Stalker Sept. 3, 1946 2,421,694 Hawkins June 3, 1947 FOREIGN PATENTS Number Country Date 850,410 France Sept. 11, 1939 

